I. Field of the Invention
The present invention relates generally to a jacketed bullet.
II. Description of Related Art
Jacketed bullets are used in a wide range of firearms in both military and nonmilitary applications. In a jacketed bullet a penetrator constructed of a had material forms the tip of the bullet. A slug constructed of a material having a lower modulus is then positioned behind the penetrator and at least a portion of both the slug and the penetrator are encased in a metal jacket. The jacketed bullet is then assembled into a cartridge with a propelling charge and primer.
In order to improve the stability and accuracy of the bullet, most firearms today include a rifled bore. A rifled bore extends in a helical fashion along at least a portion of the barrel. During launch of the bullet, the rifling in the barrel imparts spin to the bullet which increases the accuracy of the firearm.
In order to ensure proper operation of the rifling and to minimize leakage of the gasses from the firing of the bullet, the outside diameter of the jacket is slightly greater than the inside diameter of the rifling. Consequently, when the bullet is loaded into the chamber, the barrel rifling engages the outer surface of the jacket and radially inwardly compresses or “engraves” the jacket. Such engraving creates a slight elongation of the slug and effectively requires energy to plastically deform the bullet. This deformation energy and related frictional losses reduces the overall muzzle velocity of the firearm.
Historically lead has been used as the material for the slug because it has a low modulus of elasticity with respect to almost every other metal and is easily deformed. Consequently, the energy stored in the bullet by engraving is very low and only minimally affects the muzzle velocity of lead core bullets.
The use of lead as the material for the slug, however, creates other problems. For example, in shooting ranges the lead content in the ground around the range may result in an unacceptable lead toxicity.
Consequently, other materials have recently been used for the slug. These other materials include, for example, copper, brass, bronze, zinc, steel, and other materials. All of these other materials, however, have an elastic modulus greater than the modulus of lead.
Thus, when using a jacketed bullet with a nonlead slug, the bullet exhibits a greater resistance to deformation during engraving as the bullet is fired. This, in turn, increases the overall work required to engrave the bullet when fired, compared to a jacketed bullet with a lead slug, which requires less deformation work to engrave the bullet during firing. This reduction of energy during firing results in a reduced bullet velocity upon exit from the gun barrel assuming, of course, all other factors are equal.